As a baritone, Ger Withag has appeared not only in Holland, but also in Germany and many other countries. Apart from his activity as a Lieder singer, he has developed to a well-known choir educator and choir conductor and enjoys himself a high reputation in the Dutch choir world. He has rendered important services, mostly at the organization of the World-Music Festival in Kerkrade. The big concerts of this festival were at the Rodahalle, with works as the Requiem of Berlioz (with participation of the Städtischen Chores Aachen) and the Requiem in D minor by of L Cherubini under co-operation of the Limburgischen Sinfonieorchesters (LSO - Maastricht).

Ger Withag was for a long time director of choir of the Koninglijke Kerkraads Mannenkoor St. Lambertus. For many years he also co-operated as a director of choir and conductor with the Koninklijke Zangvereniging Venlona in Venlo and the Brunssums Mannenkoor.

A regular and successful co-operation between Ger Withag and the Städtischen Chor Aachen exists for more than 25 years, including many of concerts together with his choir in Holland (Kerkrade, Venlo), Belgium (Luettich) and in Aachen.